Volume shifts with partial submersion of isolated lung lobes

When an isolated lung lobe is partially submerged, volume moves from the submerged part to the unsubmerged part. We partially submerged isolated dog lobes of known weight and volume, and measured airway pressure and, by water displacement, the volume of the submerged part. The lobe was then air-dried and sectioned at the waterline and each part weighed. Multiplying lobar volume by the fractional weight of the submerged part yielded the volume of the submerged part before immersion, and therefore the volume shift to the unsubmerged part due to immersion. Dividing this volume shift by the immersion-induced change in airway pressure gave the compliance (Cr') of the unsubmerged part. Cr' was compared to Cr, the compliance of the unsubmerged part when it was inflated with air. Cr/Cr' was linearly related to the degree of immersion: as immersion increased Cr/Cr' fell; so when lobes were 80% immersed Cr/Cr' was 0.3--0.5, indicating that compressing the lower part of the lung made the upper easier to expand. This behavior could be explained if with immersion lung units moved from the submerged part to the unsubmerged part and this shift increased with the degree of immersion. We demonstrated that when one part of a lobe was compressed lung units moved away from the compressive force and that this movement could occur without similar movement of the pleural surace. Tissue movement probably accounted at least in part for our results.